Aerodynamic filter

ABSTRACT

The filter of the present invention continually provides the passenger compartment of a vehicle with a supply of purified air, even in the most severe environmental conditions. The filter comprises an inlet surface, an outlet surface, walls which define a plurality of passages which extend from the inlet surface to the outlet surface, and a filtration means for removing the impurities from the fluid. The filter preferably can be subdivided into a plurality of layers, including an inlet layer, an intermediate layer, an outlet layer. Each layer includes a plurality of cells, the cells having walls with a generally curvilinear shape. A plurality of the passages are preferably in fluid communication with a plurality of other passages. Surface filtration is used to remove the impurities from the fluid flowing through the passages. The impurities are retained within the filtration means which are disposed on the walls, as the fluid flows through the passages essentially unrestricted even when the removing means is saturated with impurities.

This is a continuation of the application Ser. No. 07/331,792, filedApr. 3, 1989 and now U.S. Pat. No. 5,002,597.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an aerodynamically contoured filterwhich removes foreign particles from a fluid, and more particularly, toa filter using surface filtration to remove contaminants from air, asair laden with particulates and aerosols is circulated through thefilter.

2. Background Art

Pollutants, pollen, dust particles, and other foreign particles areoften introduced in the air supply of closed rooms, such as thepassenger compartments of vehicles. The problem with air pollutants invehicles is particularly acute in high traffic densities, or in severeclimates with high contents of dust, smog, fog, industrial effluents, orthe like.

Many attempts have been made to remove pollutants, pollen, dustparticles, and other foreign particles from the air by using filtrationsystems. Conventionally, filtration devices which pass the air throughfilter media such as mats or screens are inserted in the intake channelof the vehicle cabins to filter out these contaminants. To effectivelyfilter out small particles, the mesh of the screen must be small. Thesmall mesh often becomes blocked after a short period of time, and it isnecessary to frequently clean or change the filter element. The smallmesh also produces a pressure drop, which is the major limiting factorinvolved in applying a filter in the intake duct of a ventilation systemfor a vehicle.

PCT Application PCT/De87/00489 describes a foraminous, multi-layeredfilter, impregnated with glycerine. The filter includes numerousapertures, such that the apertures of one layer are offset with respectto the apertures of the adjacent layers. However, such a filter isinadequate for vehicles equipped with air conditioning, since thereexists too great a pressure drop across the filter.

The problems enumerated above have prevented the application of anultra-fine particle filter in the ventilation system of a vehicle. Allvehicles are critically dependent upon an adequate supply of fresh airto enable proper defrosting and defogging. It is also imperative thatpeople with chronic allergic and asthmatic conditions have a continualsupply of fresh air in all driving environments. Accordingly, theinability to supply the vehicle cabin with an adequate supply of freshair can be a distinct health and safety hazard.

SUMMARY OF THE INVENTION

The filter of the present invention overcomes the deficiencies in theprior art, and is designed using the principles of aerodynamics tostreamline the flow of fluid therethrough.

The filter hereof is defined by a multi-layered body which comprises aninlet surface and an outlet surface, walls which define a plurality ofpassages which extend from the inlet surface to the outlet surface, andmeans for removing the impurities from the fluid.

The filter preferably can be subdivided into a plurality of layers,including an inlet layer, one or more intermediate layers, and an outletlayer. The fluid approaches the inlet layer, progresses through theintermediate layers, and departs from the filter through the outletlayer. Each layer includes a plurality of cells, having cell walls witha generally curvilinear shape. Each cell wall has a fluid inlet portionand a fluid outlet portion. The fluid outlet portion of a cell disposedon the inlet layer is in fluid communication with the fluid inletportion of a contiguous cell disposed on the adjacent intermediatelayer. The fluid outlet portion of a cell disposed on an intermediatelayer is in fluid communication with the fluid inlet portion of acontiguous cell disposed on the outlet layer. The cell walls combine todefine a plurality of passages, which extend from the inlet surface tothe outlet surface. A plurality of the passages are preferably in fluidcommunication with a plurality of other passages.

The means for removing the impurities from the fluid flowing through thepassages is disposed along the walls. The impurities are retained withinthe removing means, as the removing means enable fluid to flow throughthe passages essentially unrestricted even when the removing means issaturated with impurities. The removing means is a surface filtrationmedia which may be either wet or dry. If the media is wet, it ispreferred that an open-faced foam be used, such as polyurethane, whichis commonly impregnated with a non-toxic, non-reactive viscous solution.The wet media treats the incoming fluid that is heavily laden with dustparticles, pollutants, pollen, and other foreign particles. If the mediais dry, charged fibers are affixed to the side walls of the filter. Theairborne particles are attracted to the surface of the fiber, and aretrapped by a magnetic-like action the the fiber.

For a more complete understanding of the aerodynamic filter of thepresent invention, reference is made to the following detaileddescription and accompanying drawings in which the presently preferredembodiment of the invention is illustrated by way of example. It isexpressly understood, however, that the drawings are for purposes ofillustration and description only, and are not intended as a definitionof the limits of the invention. Throughout the following description anddrawings, identical reference numbers refer to the same componentthroughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the filter of the present invention,depicting a plurality of cells disposed on each of a series of layers,and each layer being spaced apart from each adjacent layer to illustratethe cell structure, and the structural interrelationship betweencontiguous cells;

FIG. 2 is a computer-generated skeletal perspective view of a portion ofthe filter of FIG. 1, depicting a cell disposed on a first intermediatelayer and the four cells disposed on an adjacent intermediate layer;

FIG. 3 is a perspective view of a portion of the filter of FIG. 1,depicting a first pair of cells disposed on the inlet surface or layer,portions of a second pair of contiguous cells aligned on a firstintermediate layer, and portions of a third pair of contiguous cellsaligned on a second intermediate layer;

FIG. 4 is a perspective view of a partially-sectioned cell disposed onthe inlet surface of the filter of FIG. 1;

FIG. 5 is a perspective view of partially-sectioned cell of the filterof FIG. 1 is disposed on an intermediate layer;

FIG. 6 is a bottom view of the cell of FIG. 5;

FIG. 7 is a top view of the filter of FIG. 1, the view depicting thesymmetry of the top layer and the second layer, the placement of thecontiguous cells on the second layer being depicted as hidden lines; and

FIG. 8 is a computer-generated skeletal perspective view of a portion ofthe filter of FIG. 1, depicting four cells each being disposed upon fouradjacent layers, the fluid passage being highlighted for purposes ofillustration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, FIG. 1 is a perspective view of thefilter 10 of the present invention. The filter 10 is preferably anopen-celled foam material, such as foamed polyethylene, polyurethane, orthe like. The filter 10 comprises an inlet surface 12 and an outletsurface 14, walls 30 which define a plurality of passages 40 extend fromthe inlet surface 12 to the outlet surface 14, and filtration means 60for removing the impurities from the fluid.

The inlet surface 12, walls 30, and a plurality of protruding members 70which extend into the passages 40, are preferably areodynamicallydesigned and contoured to streamline the flow of the fluid through thefilter 10. The walls 30 define a labryinth of curvilinear passages 40,each passage 40 extending from the inlet surface 12 to the outletsurface 14. Each passage 40A is in fluid communication with a series ofother curvilinear passages 40B. Each passage 40 has a generallysymmetrical configuration. Fluid entering each passage 40A is routedinto a series of adjacent passages 40B, and the fluid in passages 40A isrejoined by fluid from other adjacent passages 40B (see FIG. 8).Although the diameter of the walls 30 vary throughout the passages 40,the surface area about the passages 40 remains substantially the samethroughout the length of the passages 40.

The walls 30 surrounding the passages 40 comprise a plurality of cells50. Each cell 50 has a chute 52 extending therethrough, which is influid communication with a portion of an associated cell 50 disposed onan adjacent layer 20. More particularly, and as shown in FIGS. 4 and 5,each cell 50 is defined by a toroidal portion 54 and a chute 52integrally formed therewith. In accordance with this construction, eachcell 50 is, thus, divided into a plurality of sections 55. Each section55 is in fluid communication with a plurality of cells 50 contiguouslydisposed. As shown in these drawings, any one cell 50, thus, is placedin fluid communication with four cells 50, since there is depictedtherein, four section 55 in association with each cell 50. It isunderstood that the number of sections 55 into which each cell 50 isdivided is dictated by flow requirements, but optimally the cell 50 isdivided into a least three and, preferably four sections 55.

The filter 10 formed from the foam material, preferably is divisibleinto a plurality of layers 20, including the inlet surface layer 12, atleast one intermediate layer 22, and an outlet layer 14. The fluidapproaches the inlet layer 12, progresses through the intermediate layer22, and departs from the filter through the outlet layer 14.

Each cell 50 is preferably disposed along a layer 20. Each of the cells50 on the same layer 20 are similar in shape. In the preferredembodiment of the filter 10 of the present invention, there are threebasic cell configurations. A cell 50A disposed on the inlet layer 12 isdepicted in FIG. 4. A cell 50B disposed on any of the intermediatelayers is depicted in FIG. 5. A cell 50C disposed on the outlet layer 14is similar to the cell depicted in FIG. 4, except that there is noprotruding member 70 within the cell 50C.

The layer 20 of each cell 50 is generally normal to the axis 59 of thecell 50. The cells 50 are generally evenly spaced on each of severallayers 30. In the preferred embodiment of the present invention, all ofthe cells 50 are disposed on four layers 20, as shown in FIG. 1.

The walls 30 of the filter 10 have a generally curvilinear shape. A cellwall 30 disposed on the inlet layer 12 has an inlet portion 53 and anoutlet portion 56. The inlet portion 53 is tapered inwardly, and theoutlet portion 56 is tapered outwardly. For cells 50B disposeddownstream of the inlet surface 12, the inlet portion 53 is co-extensivewith the outlet portion 56 of the upstream cell.

FIG. 2 depicts a first pair of cells 50A disposed on the inlet surface12, portions of a second pair of contiguous cells 50B aligned on a firstintermediate layer 20A, and portions of a third pair of contiguous cells50B aligned on a second intermediate layer 20B. The cells 50A disposedon the inlet surface 12 have both an inlet portion 53A and an outletportion 56A, whereas the downstream cells have an inlet portion 55Bwhich is coextensive with the outlet portion 56A of the upstreamcontiguous cell 50A. FIG. 3 depicts a cell 50A disposed on the inletlayer 12 and a contiguous cell 50B disposed on an intermediate layer20B. Each cell 50 is in fluid communication with preferably eitherthree, four, or six cells 50 contiguously disposed along an adjacentlayer 20, although all of the drawings depict a cell 50A adjoining fourcontiguous cells 50B.

The filter 10 preferably has a 36% porosity and 0.35 inch layer spacing.Preferably, the filter 10 has four layers, the inlet surface layer 12,the intermediate layer 13 and the outlet surface layer; beingsubstantially of the same thickness, and the filter 10 having a totalthickness of between one and one-and-a-half inches. A chute 52 extendsthrough each cell 50, and a central axis 59 extends through each chute52. The axis 59 of each cell is preferably normal to the inlet surface12 and the outlet surface 14, enabling a tangential flow of air througheach of the passages 40.

Each cell 50, except for those cells 50C disposed on the outlet layer,has a contoured protruding member 70 extending therein. The protrudingmember 70 is generally symmetrical about the cell axis 59. The tip 74 ofthe protruding member 70 extends into the proximate center of the cell50. As shown in FIG. 4, the cell wall 30 has a generally curvilinearcross-section. Since each cell 50A feeds four contiguous cells 50B, theprotruding member 70 is formed by four edges 72 which divide the chute52 into four quadrants which peak at the center of the cell 50. Theprotruding member 70 deflects the fluid through the outlet portion 56Aof the cell 50A, and into the inlet portion 55B of the contiguous cells50B.

FIG. 7 is a top view of the filter 10, the view depicting the symmetryof the inlet layer 12 and an adjacent intermediate layer 20A, theplacement of the contiguous cells 50 on the intermediate layer 20A beingdepicted as hidden lines.

The filtration means 60 for removing the impurities from the fluidflowing through the passages 40 is disposed along the walls 30. Theimpurities are retained within the filtration means 60, and thefiltration means 60 enables fluid to flow through the passages 40essentially unrestricted even with the filtration means 60 is saturatedwith impurities. The filtration means 60 is a surface filtration mediawhich may be either wet or dry. If the media is wet, it is preferredthat an open-faced foam be used, such a polyurethane, which is commonlyimpregnated with a non-toxic, non-reactive viscous solution. The wetmedia treats the incoming fluid that is heavily laden with dustparticles, pollutants, pollen, and other foreign particles. If the mediais dry, charged fibers are affixed to the side walls of the filtrationmeans 60. The airborne particles are attracted to the surface of thefiber, and are trapped by a magnetic-like action to the fiber. Thefunction of the filtration means 60 is to capture the contaminants andnot allow them to rebound back into the fluid stream after striking themedia.

Most of the filtration occurs between the outlet portion 56A of one cell50 and the inlet portion 55B of a contiguous cell 50. The contoured wall30 of cell 50 guides the flow of air into the contoured inlet portion ofthe contiguous cells. The air tends to cling to the contoured cell walls30 of each cell, much as juice clings to the surface of a pitcher as itis poured therefrom. This phenomenon is well known in avionics as theCoanda Effect. Hence, the contoured cell walls 30 guide the fluidthrough the passages 40.

The filter 10 does not pass the fluid through the media, as "surfacefiltration" is more dominant than "depth filtration". The primarymechanisms involved in the filtration through the filter of the subjectinvention are "inertial impaction", "flowline interception", "diffusiondeposition", "electrostatic deposition", and "London-van der Waalsdeposition", all of which are well-known phenomena to one skilled in theart.

"Inertial impaction" is caused by the fluid changing flow direction,which results in a curvature of the streamlines. The inertia of theparticles prevents the particles from passing through the passages 40unimpeded. The inertia thrusts the particles into the contoured walls30, where the particles are deposited. The intensity of this mechanismincreases with increasing particle size and increasing flow rates.Particles are also collected by "flowing interception". The particle mayfollow the streamline of the fluid and be collected without "inertialimpaction" if the streamline is within close proximity to the collectingbody.

The trajectories of individual small particles do not coincide with thestreamlines of the fluid because of "Brownian motion". With decreasingparticle size the intensity of "Brownian motion" increases and, as aconsequence, so does the intensity of "diffusion deposition".

Aerosol particles and the fibers of a filtration media 60 generallycarry electrostatic charges that considerably influence particledeposition. Charged fibers and particles influence the filtrationprocess by altering particle trajectories and by alternating particleadherence to filter media surfaces. When the distance between a particleand the collecting body is small, deposition is influenced by London-vander Waals intermolecular forces.

If the media is wet, it is preferred that an open-faced foam be used,such as polyurethane, which is impregnated with a non-toxic,non-reactive viscous solution such as glycerine, petrolatum, grease,ethylene glycols, or edible oils. The wet media treats the incomingfluid, preferably air, that is heavily laden with dust particles,pollutants, pollen, an other foreign particles. To trap smallerparticles from the fluid stream, silicon dioxide, aluminum oxide,zeolite, diatomaceous earth may be added to the viscous solution.Chemisorption masses like citric acid, tartaric acid, calcium chlordie,sodium carbonate may also be added to remove odors and harmful acidicand alkaline contaminants.

The preferred dry media is fibers which have positive and negativeembedded charges. The preferred fibrous material is Filtrete_(R), whichis a registered trademark of the 3M Company. The fibrous material may besprayed or molded onto the contoured side walls. Airborne particlesunder 5 microns are naturally attracted to the surface of the fiber, andare trapped by a magnetic-like action to the fiber.

The filter 10 is a laminated structure, which may be precision molded,or formed by any other similar manner. The layers 20 are securedtogether by any of a variety of chemical adhesives that are well knownin the art. The cells 50 disposed on each layer 20 would require aseparate mold. Alternate layers 20A are out of phase with adjacentlayers 20B (see FIG. 6), and the alternate layers can be formed by thesame molds.

Typically, air approaches the filter 10 at a flow rate of about 20 to 30feet per second, and the air leaves the filter 10 at from 50 to 70 feetper second. The pressure loss through the filter 10 is independent ofthe number of layers 20, but is primarily dependent upon the velocity ofthe air departing from the filter 10. The number of layers 20 is notlimited by pressure drop, but is limited by the space for the filter 10in the fluid line, and the duration that the filter 10 is to remain inthe line until it will be replaced.

The tangential flow through the cells 50 serves to accelerate the air.Typical pressure drop through the filter 10 varies from 2 to 3 percent.The impurities are retained within the filter 10, and purified air flowsout from the outlet surface 14 of the filter 10.

While the aerodynamic filter 10 has been described in conjunction with aspecific embodiment, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the disclosure herein. It is intended that all suchalternatives, modifications, and variations are included herein thatfall within the spirit and scope of the appended claims.

We claim:
 1. A method of filtering air containing impuritiescomprising:(a) passing the air to be filtered through a filter, thefilter comprising:(1) an inlet surface and an outlet surface, the inletand outlet surface being separated by a distance; (2) a plurality ofcurvilinear walls, the curvilinear walls defining a plurality of fluidpassages, the fluid passages extending from the inlet surface to theoutlet surface; and (3) filtration means for removing impurities fromthe air flow through the passages, the impurities being retained inassociation with the filtration means, the filtration means enabling airto flow through the passages essentially unrestricted even when thefiltration means is saturated with impurities; the air to be filteredpassing from the inlet surface to the outlet surface thereof throughpassages thereof, and wherein the air enters the filter at a firstpressure and the air departs from the filter at a second pressure, thedifference between the first pressure and the second pressure defining apressure drop, the pressure drop being essentially independent of thedistance between the inlet surface and the outlet surface.
 2. The methodof claim 1 which further comprises:diverting a portion of the air to befiltered from one passage into another passage.
 3. The method of claim 1wherein the filter includes a plurality of layers, the air to befiltered passing through the plurality of layers.
 4. The method of claim1 wherein the filtration means is wet surface filtration means.
 5. Themethod of claim 1 wherein the filtration means is a dry surfacefiltration means.